I left the patch to dry for an hour while I had tea. Pasta which was nice...I used chalk over then placed it back inside tyre.
Just to note: you don't need to wait for the patch to dry, but you do need to wait for the glue to get tacky before applying the patch.
A thin layer of glue takes 2-3 mins tops to dry, and if it doesn't look quite evenly spread (quite likely, I find) then add another thin layer, and another 2-3 mins.
Then press the patch on nice and firmly.
And chalk - nothing wrong with dust from the road or similar. It's just to stop the patch/glue sticking to the inside of the tyre, which might then wrench the patch off when pumping up/riding.